Tools employed for downhole measurement-while-drilling (“MWD”) operations commonly include multiple specialty drill collar segments joined end to end, each segment housing one or more sensors that dynamically provide data about the tool and the surrounding formation. The batteries powering the sensors are typically housed in the individual drill collar segments along with the sensors. Such batteries commonly occupy several feet of tool space that undesirably, in some applications, places segments further away from the drill bit than may be optimal. For example, sensors assisting in decisions about steering the drill bit are often more effective when placed close to the drill bit. This allows directional decisions to be made sooner than if the sensors are further away from the drill bit. Further, the operational capacity of such tools to remain downhole may often be limited by the life of the battery.
Accordingly, it may be advantageous to provide batteries in segments that are distant from the segment housing the sensors, in order to help position the sensors in a specifically desired location. Remote battery segments may also allow the use of larger batteries and thereby improve the operational capacity of various tools. In such cases, in which remote battery segments are utilized, reliable, uninterrupted, electrical communication between segments tends to increase in importance.
Connection issues between segments are not limited to electrical power considerations. Segments including the sensor portion (e.g. the “logging string”) of a drill string are often selected from a range of segment options based on needs of the particular application. The ability to interconnect multiple transmission lines (e.g., including data and other communication lines) between segments facilitates such flexibility in locating modular tool segments within the logging string. For example, increased numbers of communication channels between segments become available for transmitting logging data and receiving commands. This in turn allows sensors to be placed in segments that are distant from other segments in which, for example, a downhole-to-surface communication device has been deployed, or in which a central memory device has been deployed. The memory may receive data from the sensors for later download and retrieval when the drill string is brought to the surface.
The task of interconnecting multiple transmission lines between drill collar segments has been problematic in the MWD industry. Typically MWD tools must be designed to withstand shock levels in the range of 500 G on each axis, plus vibration levels of 25 G root mean square and pressures of 25,000 psi. The electrical connections between segments can often be the eventual point of failure. Multiple-transmission line connections are particularly susceptible to failure due to fluid (e.g., drilling fluid) ingress during MWD operations, causing shorts between the exposed surfaces of contacts. A connection that employs multiple fluid-resistant barriers would be advantageous. It would also be advantageous to minimize possible points of fluid entry into the contact area as well as to provide a connection that is inherently tolerant to small amounts of fluid ingress.
Conventional male and female electrical connectors, particularly in MWD service, have required a fairly high precision in longitudinal positioning within, for example, a tool body or drill collar, to ensure correct mating of the male and female electrical connectors when adjoining tool bodies or drill collars are assembled. Such precision is not always easy to achieve in manufacturing processes, not withstanding the availability of adjustable length barrels of calculated or set length designed to facilitate such precise longitudinal positioning. It would tend to be advantageous for mating male and female electrical connectors to include mechanisms to account for small variations in the calculated or set length of such adjustable extension barrels.
Therefore, there is a need in the art for an improved electrical connector addressing shortcomings of the prior art, including one or more of the shortcomings described above.